The US Mint has ordered an investigation into a manufacturing anomaly that has affected what is thought to be tens of thousands of its 2016 edition of the American Eagle gold bullion coin.

The issue with some of the one troy ounce coins is that the relief image on the ‘heads’ side of the coin is higher than the rim. That stops the coins stacking correctly and the affected coins and those around them can be damaged if they are forced into a stack, Coin World reported.

The US Mint, which was informed of the problem by a customer, believes that up to 63,000 coins could have been manufactured this way but said that it was a variant, rather than an error. However, the Mint has not published pictures showing the variant.

The 2016 American Eagles have been on sale since 11 January and the US Mint at West Point has now announced the release of its 22 carat 2016 American Eagle Gold Proof Coins. They will go on sale from 17 March.

There are four different coins – a one troy ounce gold coin, a half ounce coin, a quarter ounce coin and tenth of an ounce coin. The coins will also be available to buy as a set of four. There is no maximum mintage of the new proof coins, which are all sold with a certificate of authenticity.

The heads side of the coins features an image of Liberty with flowing hair and a torch in her right hand and an olive branch in her left, designed by Augustus Saint-Gaudens. The tails side, designed by Miley Busiek, shows an eagle carrying an olive branch above a nest with a female eagle and chicks inside.

The current demand for gold from both institutional and private investors suggests that sales of the new proof coins could well be strong.